As a tobacco filter which removes tars from the tobacco smoke and insures a satisfactory smoking quality, a filter plug prepared by shaping a tow (fiber bundle) of cellulose acetate fibers with a plasticizer such as triacetin is generally used. In this filter, the constituent filaments have been partly fused together by the plasticizer to be shaped so that the filter plug has an adequate firmness. Thus, use of such filter minimizes deformation of the filter when held in a smoker's mouth and does not impart unpleasantness to the smoker. By the same token, however, when such filter is discarded after smoking, it takes a long time for the filter plug to disintegrate itself in the environment, thus adding to the pollution problem.
Meanwhile, a tobacco filter made of a creped paper manufactured from a wood pulp and a tobacco filter made from a regenerated cellulose fiber are also known. Compared with a filter plug comprising a cellulose acetate fiber, these filters are slightly more wet-disintegratable and, thus, of somewhat lower pollution potential. However, in these filters, not only the aroma and palatability of tobacco smoke are sacrificed but the efficiency of selective elimination of phenols which is essential to tobacco filters can hardly be expected.
Japanese Patent Application Laid-open No. 96208/1977 (JP-A-52-96208) discloses a sheet consisting of an acetylcellulose pulp prepared in a specified manner and short staples of a thermoplastic resin. However, because this sheet is manufactured by mix-webbing the pulp and short staples and heating the resulting paper under pressure, it is high in tensile strength and elongation after immersion in water as well as in water resistance and very low in disintegratability.
Japanese Patent Publication No. 1953/1969 (JP-B-44-1953) discloses a tobacco filter which is manufactured by shaping a paper into a rod-shape. In this filter, the paper is prepared by using crimped acetate fibers having a fiber fineness of 2 to 5 deniers and fiber length of 3 to 10 mm and other beaten stuff (stock) for paper or a binder, and as examples of the beaten stuff or stock, there is mentioned a beaten pulp having a degree of beating SR of about 10 to 15. This literature mentions that such tobacco filter insures good smoking quality and filtration properties (elimination properties) of tobacco smoke. The tobacco filter has, however, a little firmness or hardness so that it is deformed when held in a smoker's mouth. Thus, such deformation imparts unpleasant feeling to the smoker as well as deteriorates filtration properties as essentially required of tobacco filters. Further, the tobacco filter as produced using crimped acetate fibers has low dispersibility in water and, hence, low environmental degradability. Moreover, such raw material is hardly fabricated into a web (paper) so that manufacturing processes of the filter becomes complicated.
Meanwhile, a binder or plasticizer may be incorporated into tobacco filters to emphasize firmness or hardness of the filters. Such filters, however, will occasionally be high-costed, or the smoking quality or wet disintegratability of the same will be sacrificed.